Research Document - 2009/001
2008 Assessment of Pollock in 4VWX+5
By H. Stone, C. Nelson, D. Clark, and A. Cook
Abstract
Fishery removals from the Western pollock stock component (4Xopqrs+5Yb+5Zc) averaged 6,000 t since 2000 and contributed 87% (3,469 t) and 81% (4,679 t) of total landings in 2006 and 2007, respectively. Assessment results were based on a Virtual Population Analysis (VPA) model for the Western Component that incorporated indices of abundance from both the summer research vessel (RV) survey (1984-2008) and standardized CPUE from the commercial fishery, excluding the most recent 4 years (1982-2004). Age 4+ (considered spawning stock) biomass has increased steadily from a low of 7,500 t in 2000 to 29,000 t in 2007, then declined to 27,000 t in 2008. The 2001 year class was estimated to be slightly lower than indicated during the 2006 assessment (12.4 million versus 14.5 million recruits) and has been the strongest at age 2 since the 1988 year class. Current prospects for the 2004 and 2005 year classes are very poor (< 1.5 million recruits). Reduced quotas and harvests, as well as increasing population biomass have contributed to a decline in fishing mortality rates on ages 6-9, which has been below the Fref of 0.2 since 2006. The range of harvest strategies in the 2009/2010 fishing year that are risk averse (25% risk of exceeding Fref) to risk neutral (50% risk of exceeding Fref) are about 3,700 t to 4,400 t, but are based on recruitment levels beyond the range of past model predictions (lower than previously observed for the time series). An alternate base model formulation was examined for projections and risk analyses which assigned the lowest observed value of age 2 recruitment for the VPA time series (3.4 million) for 2006-2008. Based on this scenario, the range of harvest strategies in the fishing year that are risk averse to risk neutral are about 4,100 t to 4,750 t for age 5+. For the 2009/2010 fishing year, there is a 50% likelihood that removals of 4,500 t would not allow for any increase in biomass, reflecting the absence of incoming recruitment. These harvest strategies are for 4Xopqrs+5Zc and would be conservative if applied to all of 4X, since an additional 300-400 t of removals have occurred from 4Xmn over the past 2 years.
Landings from the Eastern Component (4Xmn+4VW) traditionally come from the Tonnage Class (TC) 4+ sector, and have been following a declining trend, although they exceeded 1,100 t in 2007. Since 1993, much of the Eastern Component was closed to cod and haddock directed fishing, which further reduced pollock landings from that area. Summer RV survey biomass, while variable, has increased since 2006. Most of this increase is due to good catches in 4Xmn, but not in 4VW. Estimates of total mortality from the RV survey indicate a decrease in Z for 2006 and 2007 due to higher abundance in the 2007/2008 surveys; however, it is too early to tell if the situation is actually improving. While the current level of removals has allowed for some rebuilding of the Eastern Component (i.e. in 4Xmn), it is not rebuilt yet (i.e. 4V). Directed pollock fisheries for the east should proceed with caution.
With the exception of the 2007/2008 div. 4W test fisheries and, to a lesser extent, 5Z, observer coverage for pollock directed mobile gear fisheries is very low, and has been implemented largely to address management issues. Notwithstanding these limitations, most of the total catch (82-99%) is landed and counted against respective quotas for these species. Dogfish appears to be the most commonly discarded bycatch species, with other species occurring at low levels. The highest amount of discarded catch appears to occur in the mobile gear fishery for redfish (4Xpq). Bycatch discards may also occur in the 4X pollock gillnet fishery, but observer coverage is far too low (i.e. 2 trips for 2006-2008) to make any conclusions. The habitat over which the directed pollock fishery takes place is highly energetic and of high complexity. The impact of the pollock fishery on the sea floor is currently unknown. The diet of pollock from the Scotian Shelf and Bay of Fundy has shown decadal changes, with euphausiids (krill) being predominant in the diet in the 1960s, less so in the 1990s, and once again since 2003.
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